Flaw-detector carriage for introducing radioactive source into pipelines



United States Patent Inventor Miroslav Baran Prague, Czechoslovakia Appl. No. 640,541

Filed May 23, 1967 Patented Dec. 15, 1970 Assignee By mesne assignments, to

Dr. K. Saverwein Duesseldorf, Germany Priority May 27, I966 Czechoslovakia FLAW-DETECTOR CARRIAGE FOR INTRODUCING RADIOACTIVE SOURCE INTO PIPELINES 7 Claims, 2 Drawing Figs.

11s. or 104/130,

254/134 n11. c1...; 00111 23/00, B6Ib 13/10 501 FieldofSearch, i 104/138, 139; 254/134 [56] References Cited UNITED STATES PATENTS 2,604,521 7/1952 Boucher 104/138x 2,897,779 8/1959 Perkins 104/139 2,928,357 3/1960 McBride 104/138 Primary Examiner-Arthur L. La Point Assistant Examiner-Daniel F. Worth, III Attorney-Arthur O. Klein PATENTEuniclslsm 35 1 INVENTOR.

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his Afiomey ing region of the screen, which records BACKGROUND OF THE INVENTION A common technique for inspecting welds in oil and gas pipelines and the like, is known as central projection gammagraphy. In this method, a radioactive source is typically mounted within the pipe, and a radiation-sensitive film is disposed around the outer periphery of the pipe. The presence of a flaw in the pipe wall causes radiation from the source to impinge radially through the flawed portion to the surrounda permanent impression-of theflawed location.

interior of "the pipeline by, an elongated carriage that is powered by a self-contained battery and an associated drive mechanism. The carriage moves on two longitudinally separated sets of three wheels each. The wheel axles in each set are disposed 120 apart around the inner periphery of the pipe to accommodate the natural tendency of the carriage to rotate about its longitudinal axis when the wall surface of the pipe is uneven.

In practice, it has been found that in addition to the complicated drive necessitated by the above-described wheel and axle geometry, the load'on the drive wheels varies during the rotation of the carriage, thereby increasing the danger of slippage of the wheels when the pipe wall is very uneven.

SUMMARY OF THE INVENTION fore a consta'n't'load on the drive wheels. The carriage moves on two drive wheels and a third rotatable wheel longitudinally displaced from the drive wheels. Any tendency of the carriage to rotate from its preset horizontal orientation causes a weighted pendulum suspended on the carriage frame to rotate. A compensatory rotation is'imparted-to the third wheel from the pendulum through a suitable coupling to restore the frame to its horizontal orientation.

In the interest of minimizing the total weight of the carriage, the carriage battery itself may be employed as the required pendulum weight.

The carriage drive may include a gear train coupled to the battery-driven electric motor to enable the carriage to selectively move in one of two longitudinally opposite directions.

BRIEF DESCRIPTION OF THE DRAWING The nature of the'invention and its advantages will appear more fully from the following detailed description taken in connection with the appended drawing, in which:

FIG. 1 is an end view of a flaw detection carriage constructed in accordance with the invention and disposed .in a pipeline to be tested; and

FIG. 2 is a longitudinal view of the carriage of FIG. 1.

DETAILED DESCRIPTION Referring in more detail to the drawing, the improved flaw detection carriage of the invention includes a frame 8 which is normally horizontally disposed within an elongated pipe 1, the periphery of which is to be irradiated by means of a radioactive source 4 carried on the frame8. The frame is mounted for longitudinal movement within the pipe I by means of a pair of drive wheels 6-6 and a third stabilizing wheel 10. The latter wheel is centralized with respect to and longitudinally spaced from the drive wheels 6-6.

Power for the drive wheels 6-6 is generated in a suitable battery (shown generally at 7) mounted on the carriage frame 8. The battery 7 may be coupled to the drive wheels 6-6 through a reversible electrical motonhayingasuitable gear Ina fairly sophisticated apparatus of this type for inspecting l 5 large pipelines, the source is mounted in, and guided along the train 5 for effecting movement of the carriage in a selected one of two opposite longitudinal directions under the control,

e.g., of a suitably programmed, relay-actuated automatic control system 2.

The'stabilizing wheel 10 is mounted for rotation about a vertical axis and is rotatably coupled, through a bevel gear pair 3, to a weighted pendulum 9 suspended on the frame 8.

The pendulum 9, the wheel 10, and the coupling 3 cooperate to stabilize the frame 8 inthe horizontal position shown. If, for example, unevenness in the pipe 1, causes the carriage to climb up the walls of the pipe and rotate during its longitudinal movement, the pendulum 9 will be displaced from the position shown. The coupling 3will thereupon be actuated to rotate the stabilizing wheel 10 about its vertical axis in a direction which tends to restore the frame 8 to the horizontal position shown.

The stabilizing rotation of the wheel'li) in response to the pendulum movement may, of course, be brought about by I means other than the gear pair 3. For example, a reversible servomotor may be drivingly coupled to the wheel 10 and actuated by suitable means, such as a pair of mercury contacts (not shown) positioned to be engaged by the pendulum 9 when the latter is displaced during a momentary rotation on the frame 8.

A significant saving of total weight in the carriage may be effected by mounting the battery 7 on the lower end of the pendulum 9'. In this way, the battery 7 itself serves as the required weight for the pendulum. The necessity of an auxiliary pendulum weight is therefore avoided with no loss of efficiency of the arrangement depicted.

It will be appreciated that by use of the above-described arrangement, the drive wheels 6-6 are always subjected to equal loads and the center of gravity of the carriage is invariant. Moreover, the use of two drive wheels, rather than the three employed in the prior art, allows the carriage drive unit to be considerably simplified.

It will also be understood that the above-described arrangement of parts are only illustrative of the principles of the invention.

Iclaim:

1. For use in a central projection gammagraphy system, an elongated flaw detection carriage longitudinally movable within an elongated, horizontally disposed pipe, the carriage comprising:

a carriage frame normally disposed in horizontal orientation;

a pair of drive wheels carried by the frame;

a third wheel carried by the frame and rotatable about a vertical axis, the third wheel being longitudinally spaced 1 its horizonmeans comprises a reversible servomotor drivingly coupled to the third wheel, and means triggered upon a displacement of the pendulum for actuating the servomotor.

5. A carriage as defined in claim 1, further comprising a battery mounted on the frame, and means coupling the battery to the drive wheels for longitudinally moving the carriage within the pipe in a selected one of two opposite longitudinal directions.

6. A carriage as defined in claim 5, in which the moving means comprises, in combination, an electric motordriven by the battery, and a gear train coupled to the motor. V 7

I 7: A carriage as defined in claim 5, inwhich the battery is k mounted on the pendulum to constitute the pendulum weight.

gears respectively coupled to 

